Irrigating apparatus of this type generally comprises a traveling sprahyead of nozzle assembly from which the water is dispersed over a wide path, a hose connected to this assembly and adapted to be wound upon a hose reel or drum, usually in a plurality of layers, and a water-powered drive mechanism connected to the drum or reel for winding up the hose on the drum and thereby drawing the nozzle assembly along a linear path between its original location and the drum while water continues to be dispensed from the nozzle assembly over a swath which can be both of considerable width and of considerable length.
The drive means associated with the drum can be provided with a piston motor controlled by a slide or valve which alternately shifts the water pressure to opposite sides of the piston of this motor. The water line connected to this valve and to the motor can be provided with a throttle which is controlled to establish the hose takeup torque and therefore the hose takeup speed at least initially.
Irrigating units of this type have been found to be highly advantageous because of their low cost and comparatively compact construction. They are generally placed by a tractor which can tow the reels or drums along to pay out the hose or which can tow the nozzle heads away from the hose drum.
For uniform irrigation it is important that the velocity with which the nozzle head moves along its path from its starting position of the drum be as uniform as possible. There are many influences upon the windup speed or recoiling speed of the drum which must be taken into consideration. For example, as the hose is drawn in, the frictional retardation between the hose and the ground diminishes and for a given force applied to the drum, the windup velocity tends to increase.
As the layers of the hose build up on the drum, moreover, the peripheral speed of the outermost layer increases as a result of the greater distance from the drum axis. Thus, for a given angular velocity of the drum, the windup speed increases in steps as layer after layer of hose has built up on the drum.
With conventional hose takeup irrigators, therefore, the movement of the nozzle head tends to be nonuniform, ie. progressively increases as the head moves closer to the drum as layer after layer of hose builds up on the drum. Since the amount of water discharged per unit time from the nozzle tends to be more or less constant in such systems, the successive portions of the path of the nozzle, because of the increased velocity at which the hose is wound up, receive less water than the starting portions of the path and there is, in general a nonuniform distribution of water.
French Pat. No. 2,179,596 describes an irrigating apparatus which provides a transverse bar responding to the build up of layers of hose on the drum and which becomes more and more inclined with the increasing effective diameter of the drum or the hose coil and acts upon a slide to reduce the quantity of water fed to the working cylinder and thereby diminish the angular velocity of the drum as layers tend to build up on the latter. With each jump in effective diameter, corresponding to an increased layer, there is a sudden drop in the velocity of the drum. The movement of the irrigating head thus tends to be discontinuous and the entire apparatus is subjected to sudden influences which reduce its effectiveness.